Sensor device and system having a conveyor and a sensor device

ABSTRACT

A sensor device having a sensor arrangement for detecting moving objects that includes a sensor and an electronic unit. The sensor arrangement is designed to detect an object and to subsequently investigate whether there are present within the surface of the object regions that move at a different speed and/or acceleration. The sensor arrangement can also investigate whether the object is accelerating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2008/001166, filed Feb. 15, 2008, which designated the UnitedStates, and claims the benefit under 35 USC §119(a)-(d) of GermanApplication Nos. 10 2007 011 221.3 filed Mar. 6, 2007 and 10 2007 013299.0 filed Mar. 16, 2007, the entireties of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to a sensor device comprising sensor means and anelectronic unit for detecting moving objects, a system having a conveyorfor transporting objects, and a sensor device.

BACKGROUND OF THE INVENTION

Industrial production devices frequently comprise robots or machinesthat are supplied automatically with the material to be processed via aconveyor. Such robots or machines regularly constitute a danger areathat is to be monitored with the aid of safety devices. In this case, itis usually necessary for the safety device to be capable ofdistinguishing the material inflow to the robot or to the machine frompersons whose approach to the robot or the machine is not permitted.

There are many solutions in the prior art where reference objects andreference scenes are stored and it is possible during the operation toestablish any difference of a current scene from a reference. Somesolutions store reference objects whose approach to a danger area ispermitted. By contrast, others store the reference objects or scenesthat can lead to a dangerous situation and consequently require aspecific reaction of the machine or the robot.

German Laid Open Patent Application No. 44 11 448 A1 discloses athree-dimensional measuring device with the aid of which it is possibleto detect a contour function of an object and compare it with a storedreference contour. A prescribed reaction of the system can be institutedas a function of how the measured contour matches or does not match astored contour.

The determination of a contour and its matching with a reference contourcan never be carried out completely, since every new object requiresdetection of a reference contour in a learning process.

SUMMARY OF THE INVENTION

The invention is based on the object of configuring the monitoring ofprescribed, in particular dangerous areas with regard to people, forexample, to be comparatively easier.

The invention firstly proceeds from a sensor device having a sensorarrangement for detecting moving objects that comprises sensor means andan electronic unit. The core of the invention resides in the fact thatthe sensor arrangement is designed to detect an object and tosubsequently investigate whether there are present within the surface ofthe object regions that move at different speeds.

This mode of procedure is based on the finding that objects and livingbeings, in particular people, have characteristic movement patterns.Objects normally move with reference to their surface with a homogeneousspeed or acceleration, independently of whether they are beingtransported with the aid of a conveyor or are moving automatically. Bycontrast, people cannot move without surface regions of the personhaving different speeds and accelerations. For example, one leg of aperson moves, whereas the other will be standing on a substratum. Thisdifference in speeds or accelerations of the object surface can bedetermined and used to distinguish an object from a person and/or ananimal in a comparatively simple way. On the other hand, the detectionof an acceleration of the object can already be sufficient to assignsuch a detection to a person. The point is that objects transported on aconveyor do not normally accelerate as they approach. As soon as anacceleration is detected, for example by a temporal comparison of imagesof the object, a signal can be output. The known possibilities can alsobe combined in order to be able to undertake a differentiation ofobjects.

In another embodiment of the invention, the sensor arrangement isdesigned to output a signal, in particular an alarm signal in the eventof the detection of various speeds and/or accelerations for differentregions within a surface of an object when the speeds or accelerationsdiffer by a predetermined amount. A further criterion can be taken asthe size of the region having a different speed or acceleration withreference to the object surface visible to the sensor means. Forexample, a region that has another speed or acceleration must constitutein relation to the remaining object surface a minimum proportion of theobject surface visible to the sensor means. It is conceivable to fix thesize of the region to greater than 5%, in particular greater than 10%.

It is preferred, furthermore, when the sensor arrangement is designed todetermine an image of the object with distances from the object surface,that is to say a “distance map”. If a plurality of such images areacquired one after another, it is possible to use the difference in theimages, that is to say the distances, to determine a speed oracceleration by relating the individual differences to the running time.A speed map or acceleration map of the relevant object surface can bedetermined therefrom. It is easy to determine from these data regions onthe object that have another speed or acceleration by comparison withother regions of the object. If the difference in speed or accelerationexceeds a prescribed measure, it is possible to infer the movement of aliving being, in particular a person.

In order to determine a speed image or acceleration image, it ispreferred to use a prescribed number of distance images that arerecorded one after another in time in such a way that a new image alwaysreplaces the oldest image of the prescribed group, in order to determinetherefrom the speed or the acceleration of individual pixels, inparticular. A current speed or acceleration is thereby determined in aprogressive iteration.

Three images 1, 2 and 3 are used by way of example to calculate thespeed. A fourth image is used for the next step, but the first image isno longer taken into account for the renewed calculation of the speeds,but rather then the images 2, 3 and 4.

In another embodiment, the sensor means comprise a single monitoringsensor, for example a 3D camera. Different technologies can be used todetermine a 3D image. For example, a three-dimensional image of anobject is determined by triangulation on the basis of two single stereocameras. Moreover, radar sensors or sensors that are based oninterferometry can be used. It is likewise conceivable to use a sensorthat determines a distance from a point from the propagation time orphase shift of a signal. For example, a sensor can be used in the caseof which an electromagnetic wave of specific frequency is modulated ontoa signal, it being possible to determine a distance from the object fromthe phase difference of the emitted modulated signal in relation to thesignal retroreflected by an object. This technology can also be appliedin a matrix camera such that a “distance image” of an object can beproduced.

In another embodiment of the invention, use is made of a light curtainhaving a plurality of transmitters and receivers that extends in themovement direction. An acceleration of an object can thereby beacquired.

In order, for example, to avoid the possibility of persons neverthelessreaching a danger area unobserved, because they are covered by anarticle that is likewise approaching, it is possible to use monitoringsensors, for example a plurality of 3D cameras.

By way of example, two 3D cameras are arranged such that they have anoverlapping observation area. In this case, the 3D cameras arepreferably arranged opposite with reference to a region to be monitored.It is possible thereby, by way of example, to acquire the front side andthe rear side, but also the lateral regions of an article such that aperson approaching without authorization is not shaded by this articlein such a way as no longer to be acquired.

It is likewise possible to operate at different times. In particular,the monitoring sensors, for example cameras, are synchronized with oneanother in such a way that each camera is active in a predetermined“time window”. Mutual disturbances between the sensors can thereby beavoided. A mutual influence can also be circumvented by having thesensors operate at different frequencies. In the case of a 3D sensorthat evaluates a phase shift of modulated light, different frequenciescan be related to a carrier frequency or a modulation frequency.

In order to prevent a person who is moving very slowly from reaching thedanger area, the detection of a slow movement is preferably assigned toa person detection.

In another embodiment of the invention, correction means are provided inorder to be able at least approximately to compensate speed differencesand/or acceleration differences of points in a plane at an objectsurface that moves in a normally occurring preferred direction relativeto the sensor means. This mode of procedure is a basis for the fact thata plane that is moving toward a camera does not have the same speedand/or acceleration at all locations. A point lying on the optical axisof the camera system moves more quickly toward the camera than a pointthat is at a distance from the optical axis. This dependence ispreferably compensated. To this end, a learning mode may be applied inorder to establish the transport direction and the speed of a conveyor.The transport direction can serve to define a Cartesian coordinatesystem that lies exactly in the transport direction. All recorded imagescan then be transformed into this coordinate system, something whichsimplifies the calculation of the speed or the acceleration of objectsurfaces when the system is in the regular observation mode. It ispossible in this way also to compensate the detection of an accelerationof points on an object that is actually moving constantly for pointsthat are at a distance at right angles from the optical axis of thesensor means and therefore have another acceleration than that in theoptical axis.

It is preferred, furthermore, when the sensor arrangement is designed insuch a way that it is possible to qualify regions having a differentspeed and/or acceleration on an object surface with reference to knownspeed patterns and acceleration patterns, respectively. It is therebypossible in principle, for example, to essentially identify objects andthus distinguish people from dogs that, if appropriate, are notpermitted to enter a region in contradistinction to people.

In order, for example, to be able to detect a person sitting still on apallet who is approaching a danger area by a conveying device, it isadvantageous when the sensor arrangement is capable of detectingobjects, by way of example with the aid of contours, for example bymeans of curved lines. In this case, however, this is codirected only inthe case when otherwise approaching objects have no curved lines.

In conjunction with a conveyor, it is preferred, besides, when theconveyor moves nonuniformly. A person otherwise standing still on theconveyor is thereby forced to carry out compensation movements, theresult being, once again, surface patterns having different speeds thatcan be assigned according to the invention to animals or a person.

In another embodiment of the invention, the sensor arrangement iscapable of detecting speed patterns and/or acceleration patterns withthe aid of one or more learning runs. The sensor arrangement can haverecourse to these patterns in order to undertake a comparison with acurrent speed or acceleration pattern. By way of example, it is therebypossible to distinguish a person from an animal.

The point is that an animal is known from experience to deliver adifferent pattern than a person.

Furthermore, it is preferred for the sensor arrangement to be capable ofhiding one or more prescribable subregions of the detection region inorder to output a signal. For example, only specific “volume regions”are considered in three-dimensionally acquired space as a function of aspeed or an acceleration of an object.

In another embodiment of the invention, the signal output is dependenton which position, which distance from the camera, which movementdirection, which speed and/or which acceleration objects have. Forexample, it is possible to dispense with a signal output in the case ofa large distance of an object or of a small distance of the object, andof comparatively low speed of the object.

An inventive sensor device can be applied in relation to a danger areanot only in the context of a conveyor system. It will also be possibleto control the access to a door or a gate to the effect that onlyobjects having a prescribed acceleration and/or speed pattern are givenaccess to a specific space or, in general, that the approach or passageof a person is established. It is possible thereby to control a doormovement in a way that the door does not close when the sensor deviceestablishes there are persons in the closing region of the door.

BRIEF DESCRIPTION OF THE DRAWINGS

A plurality of exemplary embodiments of the invention are illustrated inthe drawings and explained in more detail below with indication offurther advantages and details.

FIG. 1 shows a robot cell with a conveying device for bringing uparticles, in a schematic plan view;

FIG. 2 shows a robot cell, corresponding to FIG. 1, with a conveyingdevice in the case of which a person instead of an article moves towardthe robot cell;

FIG. 3 shows in a schematic plan view a robot cell with a conveyingdevice that is monitored by two cameras instead of one;

FIGS. 4 and 5 show the embodiment according to FIG. 3 in differentoperating states, likewise respectively in plan view; and

FIG. 6 shows a further embodiment of a robot cell with a conveyingdevice and two monitoring cameras in a schematic side view.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a robot cell 2 in front of which there is arranged aconveyor belt 3 for supplying it with articles 7. The robot cell 2 hasan access area 2 a that people may not pass as long as a robot 2 b isactive.

FIG. 1 illustrates a situation in which an article 7 is beingtransported on the conveyor belt 3 in a danger area 4 of the robot 2 bover the access area 2 a. A 3D camera 1 determines the speed of thearticle 7. The 3D camera 1 comprises, for example, an optical sensorwhich determines the distance from an object optically by using the“time of flight” or, for short, “TOF” method. In this case, light isemitted from a light source onto which an oscillation is modulated.Moreover, a sensor is provided with the aid of which the modulated lightcan be acquired when it is retroreflected by a corresponding surface.The distance from the object at which the light was retroreflected canbe determined from the phase difference of the oscillation modulated onbetween the emitted and the received reflected light. In order to enablea unique evaluation, the wavelength of the oscillation modulated ontothe light should be greater than twice the distance from the object atwhich the light is retroreflected. It is preferred to use a sensor witha large number of pixels, in particular a matrix sensor, that canproduce a “distance image map” of the article 7. If a plurality ofconsecutively recorded distance images are compared with one another anddivided by the time, the speed of the approaching article 7 can bedetermined with a resolution that permits the detection of differencesin speed within the surface of the article 7.

Since, however, the article 7 has a speed distribution of its surface 7a that is acquired by the 3D camera 1 and is substantially homogeneousin accordance with a solid article, the article 7 is permitted to moveinto the danger area 4. In this case, the robot 2 b in the robot cell 2continues to operate.

Provided in front of the access area 2 a, the mechanical safety devices6 that are used to prevent people from entering the danger area 4without the camera 1 being capable of perceiving this.

FIG. 2 shows a situation in which a person 8 is attempting to enter thedanger area 4. With reference to the trunk, the 3D camera 1 detectsdifferent speeds of legs 8 a, 8 b and arms 8 c, 8 d when the person 8walks up.

The robot 2 b is prompted to cease dangerous actions on the basis of theinhomogeneous speed distribution by means of an appropriate controller(not shown in the drawings).

The field of view of the respective single camera 1 in FIGS. 1 and 2 isprovided with the reference symbol 5.

Two cameras 1′, 1″ are preferred when it is possible that a person 8 maybe hidden behind or in front of the article 7, and access to the dangerarea 4 is possible in this way. The two cameras 1′, 1″ areadvantageously installed in such a way that the complete surface 7 a ofthe article 7 can be monitored. Every hidden person 8 who moves at theside of the article 7 is therefore detected.

FIG. 3 shows a situation in which only an article 7 enters the dangerarea 4, there being no person. With the robot running, the article 7 isnot prevented from moving into the danger area 4.

By contrast, FIGS. 4 and 5 illustrate a situation in which a person 8 islocated in front of or behind the article 7 and wishes to enter thedanger area 4 in this way. However, at least respectively one camera 1′,1″ is capable of seeing the person 8 and appropriately identifying thesame, and so appropriate measures may be instituted in the robot cell 2before the person enters.

FIG. 6 shows an embodiment in a side view that can appear in plan viewjust like the embodiments in accordance with FIGS. 3 to 5, in the caseof which the two cameras 1′, 1″ cannot see. Monitoring fields 5′, 5″,which are also indicated in FIGS. 3, 4 and 5, indeed intersect oneanother, but the monitoring fields in each case do not include the othercamera 1, 1″.

This has the advantage that opposite cameras 1′, 1″ do not cause mutualdisturbance when they are detecting because, for example, the respectiveillumination of the camera comes to be influenced. An adequatereliability of detection is thereby ensured for the respective camera.

Since, unlike in known embodiments, people are not detected by theirshape or contour, but are detected by analyzing a speed distributionthat can be determined with comparative ease with aid of a 3D camera,this results in a comparatively simple and reliable system. However,this is also due to the fact that in determining a speed distributiondetection is not influenced by the clothing, hats or baggage that theperson is wearing or carrying along.

The use of two cameras prevents “viewing shadows”, and so it is reliablypossible to prevent a person from entering the danger area of the robotor of the machine while hidden by an article.

LIST OF REFERENCE SYMBOLS

-   1 3D camera-   1′ 3D camera-   1″ 3D camera-   2 Robot cell-   2 a Access area-   2 b Robot-   3 Conveyor belt-   4 Danger area-   5 Field of view of the camera-   5′ Field of view of the camera-   5″ Field of view of the camera-   6 Safety device-   7 Article-   7 a Surface-   8 Person-   8 a Leg-   8 b Leg-   8 c Arm-   8 d Arm

1. A sensor device having a sensor arrangement for detecting movingobjects, said device comprising a sensor and an electronic unit, whereinthe sensor arrangement detects an object and subsequently investigateswhether there are present within a surface of the object regions thatmove at least at one of a different speed and a different acceleration.2. The sensor device of claim 1, wherein the sensor arrangement detectsan object and subsequently investigates whether the object isaccelerating.
 3. The device of claim 1, wherein the sensor arrangementoutputs a signal when it detects a difference in at least one of speedand acceleration of regions of the object that exceeds a predeterminedvalue.
 4. The device of claim 1, wherein the sensor arrangementdetermines an image of the object with distances from the objectsurface.
 5. The device of claim 1, wherein the sensor arrangementintercompares distance images recorded by the sensor in order to findregions of an object surface that have at least one of different speedsand accelerations.
 6. The device of claim 1, wherein the sensorarrangement determines distance differences from a comparison ofdistance images, and determines at least one of a speed image and anacceleration image of the object by reference to a time scale.
 7. Thedevice of claim 1, wherein a prescribed number of distance images areused iteratively by the sensor arrangement in order to determine atleast one of a speed image and an acceleration image.
 8. The device ofclaim 1, wherein the sensor comprises a single monitoring sensor.
 9. Thedevice of claim 8, wherein the monitoring sensor is a 3D camera.
 10. Thedevice of claim 1, wherein the sensor comprises a plurality ofmonitoring sensors.
 11. The device of claim 10, wherein the plurality ofmonitoring sensors are arranged such that they have an overlappingobservation region.
 12. The device of claim 10, wherein the plurality ofmonitoring sensors are positioned in such a way that the sensors are notmutually visible.
 13. The device of claim 10, wherein the monitoringsensors are arranged opposite with reference to a region to bemonitored.
 14. The device of claim 10, wherein the monitoring sensorsoperate at different detection frequencies.
 15. The device of claim 10,wherein the monitoring sensors are active in different time intervals.16. The device of claim 1, further comprising correction means to atleast approximately compensate at least one of speed differences andacceleration differences of points on a known surface form, inparticular in a plane at an object surface that moves in a customarymovement direction relative to the sensor.
 17. The device of claim 1,wherein the sensor arrangement qualifies regions having at least one ofdifferent speeds and different accelerations on an object surface withreference to known speed patterns and acceleration patterns,respectively.
 18. The device of claim 1, wherein the sensor arrangementidentifies objects.
 19. The device of claim 1, wherein the sensorarrangement detects at least one of speed patterns and accelerationpatterns based on at least one learning run.
 20. The device of claim 1,wherein the sensor arrangement shields at least one prescribablesubregion of the detection region in order to determine signals.
 21. Thedevice of claim 1, wherein the sensor arrangement outputs a signal, thetype of which is dependent on at least one of the position, the distancefrom the camera, the movement direction, the speed and the accelerationof the object.
 22. A system having a conveying device for transportingan object and a sensor device as claimed in claim
 1. 23. The system ofclaim 22, wherein the conveying device causes a nonuniform movement ofthe object.